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Last night, the Performing Life grown-ups were at Parlana, Cochabamba’s language exchange night, selling bracelets and CDs made by the children. We also held a raffle for some rather excellent cheese! Fun was had. Balls were juggled. And a TV crew interviewed Adalid about our work, so stay tuned for that next week. Thanks to […]

Hear from our community

THE TEAM

meet
Marye

My name is Marye Dijkstra and I am from The Netherlands. From an early age I have always had a natural instinct to help other people, especially children, but above all: whole family systems. Offering disadvantaged families in less fortunate situations the opportunities to further their aspirations, goals and expectations of life. I believe it is a challenge to make people stronger and teach them to discover their own strengths and talents to change their own present and future.

In 2010 I worked for 3 months as a volunteer in a day-care center for children with special needs in Cochabamba, Bolivia. I was immediately excited about Bolivia with its authentic and special culture, nature and population. I graduated with my Master’s in pedagogical sciences in the Netherlands in 2011. After graduating, I returned to Bolivia for 1.5 years to volunteer again, this time with orphans.

Unfortunately I couldn’t volunteer forever, so I returned to The Netherlands to work two years with young adults who suffered from mental disabilities and conduct problems, but still with the plan to live in Bolivia in the future again. Then, at the end of last year, I was really happy to discover that Performing Life had a vacancy. I read a lot about the organization and I was directly feeling morally connected to their mission and goals. I love that Performing Life has a fun and cheerful method to achieve a serious purpose. I think it is exactly the right method to reach children, their families and communities. The organization has different, complementary, programs to achieve a better future for people who really need it. So, I am really lucky to be able to say that since mid-February I am working as the new National director. I am here just for two weeks right now and I already feel comfortable and really welcome in the Performing life team!

THE CHILDREN

meet
Christian

Cristian Maire
, 12, joined Performing Life (PL) in April 2012. He lives with his stepfather, mother, and older brother; he doesn’t know his father, who abandoned the family before Cristian was born. His family lives in one room in the Montenegro region, about 20 km west of Cochabamba. Because Cristian’s family has only one bed, he sleeps on the floor. Cristian’s stepfather is often verbally abusive, and worse, sometimes beats him.

It’s the undesired deviation of a periodic signalfrom the ideal timing…

Right…

OK then…

So, even though the above definition is correct, it doesn’t really let you know why jitter is bad for a digital audio signal, how jitter actually degrades the signal or what the aural effects of jitter are. Let’s take a closer look at jitter in order to answer these questions.

First, it’s helpful to understand a bit about word clock. Here’s a graphical representation of a word clock signal:

A word clock signal acts like a conductor, providing a timing signal to all the parts of a digital audio system so that each process may be triggered at a precise moment. If you think of your digital audio system as an intricate mechanical device, the word clock is analogous to the teeth of the gears that make various parts of the device move together. Think of Charlie Chaplin in “Modern Times”:

Here’s another way to think about how a digital audio system works. Start with an analog waveform:

Now, in order to digitize this waveform (i.e describe it using numbers), let’s overlay a piece of graph paper:

Using the graph, we can describe the waveform with letters and numbers:

At
A
the wave is
8;

at
B
the wave is
11
;

at
C
the wave is
14
,

at
D
the wave is
15
, and so on.

We could store these numbers and use them to recreate the waveform later. Please don’t bust our chops about the obvious inaccuracy between the red waveform and the blue points, it’s an analogy, people.

So, to forge on with the analogy, imagine that the letters are samples and the numbers are bit levels. Now we’re recording digital audio. It might look like this:

At sample 1, digital level is 0111;

at sample 2, digital level is 1011; and so on.

Notice our word clock signal at the top of the graph. It’s the signal that triggers each sample in a digital audio system.

Once we’ve recorded our waveform as numbers, we can “re-plot” the points and re-draw the waveform to get back our original signal. We’ve just recorded and played back a digital audio signal.

The process of converting our waveform to numbers is called
analog to digital
conversion – here’s what it might look like:

The process of converting the numbers back into a waveform is called
digital to analog
conversion – here’s a movie of that process.

Now, throughout this whole process we’ve assumed that the vertical lines on our graph paper are evenly spaced. Imagine that we got some faulty graph paper where the vertical lines weren’t evenly spaced and we attempted to re-draw our waveform using the numbers we previously recorded. Clearly the resultant waveform would not be like the original:

Look at the top of our graph, that’s what a jittery word clock looks like. Notice that the distance between the transitions is uneven – this is jitter.

Though we’ve greatly exaggerated the amount of jitter in this graphic, it does show how a jittery word clock causes samples to be triggered at uneven intervals – this unevenness introduces distorsion into the waveform we’re trying to record and reproduce.

For another take on jitter, let’s think again about Charlie Chaplin and “Modern Times”. A film functions in a similar manner to digital audio, in that a film camera doesn’t record every instant of a scene, but rather “samples” a scene by taking a series of still pictures at a fast enough rate to fool the eye into thinking it sees fluid movement. As you can imagine, the regularity of the exposure (and subsequent projection) of film frames is crucial to maintaining the illusion of fluid movement. Back in the days of Chaplin, early film cameras weren’t so even – frame jitter made the movement seem jerky and unnatural.

If jitter gets into our D-to-A stage, it degrades the playback. The original digital recording is intact, and we just need to remove the jitter or get a better D-to-A converter to resolve the issue. Going back to our film analogy, if our projector is uneven, our film is probably fine, we just need a better projector.

On the other hand, if jitter gets into the A-to-D stage, those errors are “baked into” the digital data – there’s no recovering the original waveform. If you’ve shot your film with a hand cranked film camera, there’s no way you’re getting that jerky motion out of the film. This is why getting the A-to-D stage of a digital recording system right is so crucial.

So, what does digital audio affected by jitter sound like? To answer this question, imagine a recording of an orchestra made with a perfectly placed stereo pair of mics. If you listen to the analog output of the mic pres, ideally you’ll have a precise and wide image of the orchestra. If you closed your eyes, you could point to the triangle player, there, behind the second violins.

Smaller amounts of jitter start to cloud the precision of the stereo image – you can’t pinpoint sources as clearly. As greater amounts of jitter degrade the system, the stereo image starts to shrink – your orchestra isn’t so wide. With increasing jitter, changes in timbre occur that accentuate ugly harmonics.

To avoid jitter, use a finely engineered clock source as found in all of Apogee’s interfaces. If you’re using multiple digital devices, use a Master clock like Apogee’s Big Ben and make word clock connections using our Wide Eye cable.

It’s Summertime, But These Students Can’t Wait to Go to School

[audio:QuickPoint – 7-22-09.mp3]Click the play button to hear the audio Quick Point.

Most gradeschool children are enjoying their summer off, but some young Oregonians already have September on their minds. You see, they are on the waiting list of the Children’s Scholarship Fund-Portland and eagerly hope to attend the school of their choice next fall.

Families of greater financial means may already have quot;school choice.quot; They can move to a neighborhood with a public school they like, or they can pay for private or parochial school tuition.

But those options are often out of reach for lower-income families. Despite their willingness to sacrifice to give their children the best education they can, lower-income parents still may find their children trapped in schools that do not meet their kids’ needs. The demand for choice in education is growing. Parents want the best for their children, and private programs like the Children’s Scholarship Fund-Portland are proud to help them achieve it.

As for that waiting list? If you would like to make a dream come true this summer for a low-income Oregon child who is eager to learn and to succeed in school, visit Cascade Policy Institute on the web at
www.cascadepolicy.org
and click on the Children’s Scholarship Fund-Portland.